a countermeasure to prevent cot bottom pitting corrosion by shop primer
DESCRIPTION
A countermeasure to prevent COT bottom pitting corrosion by shop primer. 15 SEP 2006 T echnical Division Mitsui O.S.K.Lines. Inert Gas . Sludge . Oil Coat . Crude oil . Steel . Sludge, Seawater . Crude Oil . Concentrated Salt Water . Sludge . Oil Coat . Steel . - PowerPoint PPT PresentationTRANSCRIPT
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A countermeasure to preventCOT bottom pitting corrosion by shop primer
15 SEP 2006T echnical DivisionMitsui O.S.K.Lines
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Crude oil
Sludge, Seawater H2S
Oil Coat Salt Water ・ abt.8%NaCl, Salt Water Sludge ・ Solids in Oil ・ Drops from ceiling ( Sulfur , Rust ) ⇒ Cause of Pits
Crude Oil
Concentrated Salt Water
Oil Coat
Steel
Sludge
Oil Coat High Humidity ( Acid Dew ) Inert Gas condition ・ SOX , O2 containResidue of Salt Water Sludge ・ Solids in Oil ・ Sulfur , Rust
Ballast Condition
Inert Gas
Oil Coat
Steel
Sludge
Full Load Condition Cargo Tank Bottom
Pits
Cargo Tank Environment
3( the worst case 1320 pits per tank )
Photo of pits at No paint applied VLCC ( VLCC B 2919 pits per Vessel )
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No paint applied 2.5y dock 5 y dockVLCC A 1323 pits 2356 pitsVLCC B 1246 pits 2919 pits
S/P applied 2.5y dock(TMCP-YP32) VLCC C 50 pits VLCC D 44 pits (per vessel)
⇒ Better result for S/P !
Record of Pitting Corrosion NO PAINT vs SHOP PRIMER
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S/P reduced the number of bottompits dramatically (1000 to 50 !)
Shop primer seems to be remaining( very minute and hard layer !)
Measured thickness of S/P layer was about 50μm( Why did the thickness of S/P increase from 15μm to 50μm ?)
Results of onboard investigation at G. dock
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S/P did really remain even at G.dock?(about 2.5 year after delivery)
S/P seems to be effective in reducing the number of bottom pits
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VLCC C JUL 2000 DeliveryVLCC D SEP 2000 Delivery
JAPAN ~ P/G trade
PAINT SPECCARGO TANK S/P 15μmSLOP TANK T/E 250μm
S/P applied D/H VLCCs
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Cutting C.O.T. bottom plate for analysis by JFE Steel
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SEM Cl S
Fe O Zn200μm
High
low
⇒ Minute layer including iron and zinc oxide has been formed on the steel plate
EPMA analysis of shop-primer layer at the VLCC COT bottom
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Not at all the simplest effect of zinc-anode
But the layer of iron-and-zinc-oxide, hard, minute and more anti-corrosive in nature than pure iron-oxide, has been considered formed
Conclusion
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New Record of Pitting CorrosionTable No. of Pits ( Depth 4mm over 、 per vessel )
Bottom Spec.
TANKER2.5Y-dock
5Y-dock7.5Y-dock
10Y-dock
12.5Y-dock
No Paint
VLCC A1323 pits
2356pits
1082pits
- -
VLCC B1246 pits
2919pits
- - -
ShopPrimer
VLCC C 50 pits213 pits
- - -
VLCC D 44 pits 61 pits - - -
VLCC E 88 pits 39 pits - - -
Suez Max. Tank - - -
47 pits
684 pitsNo. of Pitting Corrosions are still very few
At 5years after deliveryShop Primer is still effective in reducing pits on bottom
※Pits of Suez Max. Tank. are depth 3mm over
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S/P still reduced the number of bottompits dramatically (1000-2000 to 50 !)
Shop primer seems to be remaining
Results of onboard investigation at 5 years dry docking
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Cutting C.O.T. bottom plate for analysis
Photo VLCC D Sample ( No.4 COT ( P ) ) Photo VLCC E Sample ( No.2COT ( P) )
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EPMA Analysis - Zn in Rust Layer
Low← → High
Fig. EPMA Analysis ( VLCC D , C4-1 )
図 EPMA Analysisi ( VLCC E , J7-1 ) (a) COMP (b) Zn
(a) COMP (b) Zn
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Quantitative analysis – Zn in Rust
TANKERVLCC D
( 2.5years Dock )
VLCC D( 5years Dock )
VLCC E( 5years Dock )
Sample code
A0 B0 C4 D3 E3 I9 J7 K8
Element
(g/m2)
Fe205.
2243.
8234.
9235.
1406.
0242.
1270.
6316.
0
Zn 8.9 4.1 1.7 0.3 7.0 1.8 5.9 2.6
Table Fe, Zn Content
Fig. Zn Content in Rust
ICP Analysis・ Sample plate : 30×30mm ・ Dissolution of Rust
・ After 5 yearsZinc is existing in Rust0.0
2.0
4.0
6.0
8.0
10.0
12.0
VLCC D (2.5y) VLCC D (5y) VLCC E (5y)
Zn
g/m
2 )
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Summary
RESULT From Investigation into COT bottom plate「 VLCC D 」 and 「 VLCC E 」 (1) KEEP few pitting repair
Zinc primer effect is continued 5 years
(2) Zinc is still existing in the RustIi was supposed that Zinc was used up in less than 1 year. But Zinc is still existing after 5 years
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Reinforcement of Zn primer’s effect by developed steel
Decrease in 35% in pitting corrosion depth was confirmed by applying the developed steel compared with conventional steel.
Temperature controlled bath ( 50℃ )
Artificialseawater
Sample( surface: Oil-coat or Sludge )
Gas ( 5%O2+10%H
2S+N2 )
Developed steel with Zn primer⇒ Pitting depth reduction
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
Conventional Steel with Zn primer
Developed steel with Zn primer
Maxim
um
pit
tin
g
dep
th (
mm
)
Reductionabout 35%
Laboratory corrosion test simulated COT bottom
Laboratory corrosion test simulated COT bottom
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Presumption of number of repair necessary pitting corrosion
The number of necessary repair pits decreases greatly.
0
10
20
30
40
50
-1.9 2.0-
2.4
2.5-
2.9
3.0-
3.4
3.5-
3.9
4.0-
4.4
4.5-
4.9
5.0-
Pitting corrosion depth (mm)
Fre
qu
en
cy
(pit
s)
Real Pits in Tanker F Adopted developed steel
Range of repair necessary pits
Each pitting depth reduce
35%
Adopted steel
Pits depth
Conventional
Over 3.0mm 89 pits
Over 4.0mm 31 pits
DevelopedDeveloped
13 pits13 pits
0 pits0 pits
Investigation of 111 pits among 684 pits in practical tanker 12.5 years old
<111 pits>
Adopted steel
Pits depth
Conventional
Over 3.0mm 548 pits
Over 4.0mm 191 pits
DevelopedDeveloped
80 pits80 pits
0 pits0 pits
<per tanker>
684 pits/111 pits
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Effect of developed steel application in practical tanker
Fig. Number of repair necessary pitting corrosion in practical tanker bottom
0
1,000
2,000
3,000
4,000
0 5 10 15 20 25Ship age (year)
Nu
mbe
r of
nec
essa
ry r
epai
r pi
ttin
g co
rros
ion
(Pit
s)
Tanker (Zn primer)Tanker (bare)
Conventional Steel (bare)
Conventional steel with Zn primer
Developed steelWith Zn primer
The number of necessary repair pitting corrosion decreases greatly by the Zn primer application.
In addition
The number of necessary repair pitting corrosion decreases more
greatly by applying the developed steel.
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《 Acid salt water dip corrosion test 》 Sample : Conventional steel, Developed steel Solution : Sulfuric acid (20%) and NaCl ( 3%) Temp. : 40℃ Test time : 6 hours Evaluation: Corrosion speed
In very severe acid environmentCorrosion speed : Reduction to about 10%
Temperature controlled bath ( 40℃ )
Sulfuric acid + NaCl solution
Sample
It is thought that the application of the developed steel is effective to high acidity part in ship.
(Reference) Acid examination result of development steel
0
20
40
60
80
100
120
Conventional SteelC
orro
sion
spe
ed (
g/m
2 hr)
Acid salt water dip corrosion test
About 90% decrease
Developed Steel
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Shop Primer is an effective pitting corrosion prevention system.
New steels are developed, They are also an effective pitting corrosion prevention system.
Combinations of Shop primer and Anti-Corrosion steel is more effective
Conclusion
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Thank you for your attention